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Welcome to Prognosis. I'm Laura Carlson. It's day 331 since coronavirus was declared a global pandemic.

Today's main story? In Chicago, after a heated negotiation, public officials and teachers' unions are getting close to an agreement about whether and when to return to in-person school.

But Chicago's flight is one that's playing out in cities all over the country.

But first, here's what happened in virus news today.

Early data suggests the Oxford AstraZeneca vaccine is only 22% effective against mild and moderate disease caused by the South African strain of coronavirus.

Astra said in a statement that there isn't enough information yet to say whether it's effective at preventing severe COVID-19 cases, hospitalizations, and deaths.

The company said work was already underway to adapt the vaccine to deal specifically with the South African variant, and that a new version could be available by the fall.

South Africa, where over 90% of new cases, are the more contagious strain first identified there, will temporarily halt the rollout of the Astra vaccine.

The country plans to accelerate its supply of shots from Johnson & Johnson and Pfizer.

Dr. Anthony Fauci warned Americans not to delay their second dose of the coronavirus vaccine.

That came, after other health experts suggested recently,

there may be a benefit to pushing more people to get a first shot and delaying follow-ups.

Fauci said the scientific data points strongly to the benefit of following

the recommended timetable for the two doses,

and that U.S. vaccine supply should improve in February and March, as the manufacturing capability escalates.

Finally, President Joe Biden said it's unlikely the U.S. will reach herd immunity for the coronavirus before the end of the summer.

Herd immunity means enough people become resistant to the disease that its spread becomes unlikely.

In the U.S., logistical delays and vaccine shortages have meant only a small fraction of the population has received shots since two different vaccines became available in December.

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